﻿using System;
using System.Diagnostics.CodeAnalysis;
using System.Security.Cryptography;

namespace AgiliTrain.PhoneyTools.Security.Cryptography
{
  /// <summary>
  /// MD5Managed: A HashAlgorithm implementation that acts as a thin wrapper
  /// around a C# translation of the MD5 reference implementation. The C code
  /// has been translated as closely as possible so that most of the original
  /// structure remains and comparisons between the two are straightforward.
  /// </summary>
  /// <remarks>
  /// Derived from the RSA Data Security, Inc. MD5 Message-Digest Algorithm.
  /// 
  /// Specification:
  /// RFC1321 - The MD5 Message-Digest Algorithm
  /// http://www.faqs.org/rfcs/rfc1321.html
  /// 
  /// Original license:
  /// Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
  /// rights reserved.
  /// 
  /// License to copy and use this software is granted provided that it
  /// is identified as the "RSA Data Security, Inc. MD5 Message-Digest
  /// Algorithm" in all material mentioning or referencing this software
  /// or this function.
  /// 
  /// License is also granted to make and use derivative works provided
  /// that such works are identified as "derived from the RSA Data
  /// Security, Inc. MD5 Message-Digest Algorithm" in all material
  /// mentioning or referencing the derived work.
  /// 
  /// RSA Data Security, Inc. makes no representations concerning either
  /// the merchantability of this software or the suitability of this
  /// software for any particular purpose. It is provided "as is"
  /// without express or implied warranty of any kind.
  /// 
  /// These notices must be retained in any copies of any part of this
  /// documentation and/or software.
  /// </remarks>
  public class MD5Managed : HashAlgorithm
  {
    // Current context
    private readonly MD5_CTX _context = new MD5_CTX();
    // Last hash result
    private readonly byte[] _digest = new byte[16];

    /// <summary>
    /// Initializes a new instance.
    /// </summary>
    public MD5Managed()
    {
      MD5Init(_context);
    }

    /// <summary>
    /// Initializes internal state.
    /// </summary>
    public override void Initialize()
    {
      MD5Init(_context);
    }

    /// <summary>
    /// Updates the hash code with the data provided.
    /// </summary>
    /// <param name="array">Data to hash.</param>
    /// <param name="ibStart">Start position.</param>
    /// <param name="cbSize">Number of bytes.</param>
    protected override void HashCore(byte[] array, int ibStart, int cbSize)
    {
      MD5Update(_context, array, (uint)ibStart, (uint)cbSize);
    }

    /// <summary>
    /// Finalizes the hash code and returns it.
    /// </summary>
    /// <returns></returns>
    protected override byte[] HashFinal()
    {
      MD5Final(_digest, _context);
      return Hash;
    }

    /// <summary>
    /// Returns the hash as an array of bytes.
    /// </summary>
    public override byte[] Hash
    {
      get
      {
        return _digest;
      }
    }

    // Return size of hash in bits.
    public override int HashSize
    {
      get
      {
        return _digest.Length * 8;
      }
    }

    ///////////////////////////////////////////////
    // MD5 reference implementation begins here. //
    ///////////////////////////////////////////////

    /* MD5 context. */
    private class MD5_CTX
    {
      public readonly uint[] state;   /* state (ABCD) */
      public readonly uint[] count;   /* number of bits, modulo 2^64 (lsb first) */
      public readonly byte[] buffer;  /* input buffer */

      public MD5_CTX()
      {
        state = new uint[4];
        count = new uint[2];
        buffer = new byte[64];
      }

      public void Clear()
      {
        Array.Clear(state, 0, state.Length);
        Array.Clear(count, 0, count.Length);
        Array.Clear(buffer, 0, buffer.Length);
      }
    }

    /* Constants for MD5Transform routine. */
    private const int S11 = 7;
    private const int S12 = 12;
    private const int S13 = 17;
    private const int S14 = 22;
    private const int S21 = 5;
    private const int S22 = 9;
    private const int S23 = 14;
    private const int S24 = 20;
    private const int S31 = 4;
    private const int S32 = 11;
    private const int S33 = 16;
    private const int S34 = 23;
    private const int S41 = 6;
    private const int S42 = 10;
    private const int S43 = 15;
    private const int S44 = 21;

    private static byte[] PADDING;

    [SuppressMessage("Microsoft.Performance", "CA1810:InitializeReferenceTypeStaticFieldsInline", Justification = "More compact this way")]
    static MD5Managed()
    {
      PADDING = new byte[64];
      PADDING[0] = 0x80;
    }

    /* F, G, H and I are basic MD5 functions. */
    private static uint F(uint x, uint y, uint z) { return (((x) & (y)) | ((~x) & (z))); }
    private static uint G(uint x, uint y, uint z) { return (((x) & (z)) | ((y) & (~z))); }
    private static uint H(uint x, uint y, uint z) { return ((x) ^ (y) ^ (z)); }
    private static uint I(uint x, uint y, uint z) { return ((y) ^ ((x) | (~z))); }

    /* ROTATE_LEFT rotates x left n bits. */
    private static uint ROTATE_LEFT(uint x, int n) { return (((x) << (n)) | ((x) >> (32 - (n)))); }

    /* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
       Rotation is separate from addition to prevent recomputation. */
    private static void FF(ref uint a, uint b, uint c, uint d, uint x, int s, uint ac)
    {
      (a) += F((b), (c), (d)) + (x) + (uint)(ac);
      (a) = ROTATE_LEFT((a), (s));
      (a) += (b);
    }
    private static void GG(ref uint a, uint b, uint c, uint d, uint x, int s, uint ac)
    {
      (a) += G((b), (c), (d)) + (x) + (uint)(ac);
      (a) = ROTATE_LEFT((a), (s));
      (a) += (b);
    }
    private static void HH(ref uint a, uint b, uint c, uint d, uint x, int s, uint ac)
    {
      (a) += H((b), (c), (d)) + (x) + (uint)(ac);
      (a) = ROTATE_LEFT((a), (s));
      (a) += (b);
    }
    private static void II(ref uint a, uint b, uint c, uint d, uint x, int s, uint ac)
    {
      (a) += I((b), (c), (d)) + (x) + (uint)(ac);
      (a) = ROTATE_LEFT((a), (s));
      (a) += (b);
    }

    /* MD5 initialization. Begins an MD5 operation, writing a new context. */
    private static void MD5Init(MD5_CTX context)  /* context */
    {
      context.count[0] = context.count[1] = 0;

      /* Load magic initialization constants. */
      context.state[0] = 0x67452301;
      context.state[1] = 0xefcdab89;
      context.state[2] = 0x98badcfe;
      context.state[3] = 0x10325476;
    }

    /* MD5 block update operation. Continues an MD5 message-digest
       operation, processing another message block, and updating the
       context. */
    private static void MD5Update(MD5_CTX context,  /* context */
                                  byte[] input,     /* input block */
                                  uint inputIndex,  // Starting index for input block
                                  uint inputLen)    /* length of input block */
    {
      /* Compute number of bytes mod 64 */
      uint index = (uint)((context.count[0] >> 3) & 0x3F);

      /* Update number of bits */
      if ((context.count[0] += ((uint)inputLen << 3)) < ((uint)inputLen << 3))
      {
        context.count[1]++;
      }
      context.count[1] += ((uint)inputLen >> 29);

      uint partLen = 64 - index;

      /* Transform as many times as possible. */
      uint i = 0;
      if (inputLen >= partLen)
      {
        Buffer.BlockCopy(input, (int)inputIndex, context.buffer, (int)index, (int)partLen);
        MD5Transform(context.state, context.buffer, 0);

        for (i = partLen; i + 63 < inputLen; i += 64)
        {
          MD5Transform(context.state, input, i);
        }

        index = 0;
      }

      /* Buffer remaining input */
      Buffer.BlockCopy(input, (int)(inputIndex + i), context.buffer, (int)index, (int)(inputLen - i));
    }

    /* MD5 finalization. Ends an MD5 message-digest operation, writing the
       the message digest and zeroizing the context. */
    private static void MD5Final(byte[] digest,    /* message digest */
                                 MD5_CTX context)  /* context */
    {
      byte[] bits = new byte[8];

      /* Save number of bits */
      Encode(bits, context.count, 8);

      /* Pad out to 56 mod 64. */
      uint index = (uint)((context.count[0] >> 3) & 0x3f);
      uint padLen = (index < 56) ? (56 - index) : (120 - index);
      MD5Update(context, PADDING, 0, padLen);

      /* Append length (before padding) */
      MD5Update(context, bits, 0, 8);

      /* Store state in digest */
      Encode(digest, context.state, 16);

      /* Zeroize sensitive information. */
      context.Clear();
    }

    /* MD5 basic transformation. Transforms state based on block. */
    private static void MD5Transform(uint[] state,
                                     byte[] block,
                                     uint blockIndex)
    {
      uint a = state[0], b = state[1], c = state[2], d = state[3];
      uint[] x = new uint[16];

      Decode(x, block, blockIndex, 64);

      /* Round 1 */
      FF(ref a, b, c, d, x[0], S11, 0xd76aa478); /* 1 */
      FF(ref d, a, b, c, x[1], S12, 0xe8c7b756); /* 2 */
      FF(ref c, d, a, b, x[2], S13, 0x242070db); /* 3 */
      FF(ref b, c, d, a, x[3], S14, 0xc1bdceee); /* 4 */
      FF(ref a, b, c, d, x[4], S11, 0xf57c0faf); /* 5 */
      FF(ref d, a, b, c, x[5], S12, 0x4787c62a); /* 6 */
      FF(ref c, d, a, b, x[6], S13, 0xa8304613); /* 7 */
      FF(ref b, c, d, a, x[7], S14, 0xfd469501); /* 8 */
      FF(ref a, b, c, d, x[8], S11, 0x698098d8); /* 9 */
      FF(ref d, a, b, c, x[9], S12, 0x8b44f7af); /* 10 */
      FF(ref c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
      FF(ref b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
      FF(ref a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
      FF(ref d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
      FF(ref c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
      FF(ref b, c, d, a, x[15], S14, 0x49b40821); /* 16 */

      /* Round 2 */
      GG(ref a, b, c, d, x[1], S21, 0xf61e2562); /* 17 */
      GG(ref d, a, b, c, x[6], S22, 0xc040b340); /* 18 */
      GG(ref c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
      GG(ref b, c, d, a, x[0], S24, 0xe9b6c7aa); /* 20 */
      GG(ref a, b, c, d, x[5], S21, 0xd62f105d); /* 21 */
      GG(ref d, a, b, c, x[10], S22, 0x02441453); /* 22 */
      GG(ref c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
      GG(ref b, c, d, a, x[4], S24, 0xe7d3fbc8); /* 24 */
      GG(ref a, b, c, d, x[9], S21, 0x21e1cde6); /* 25 */
      GG(ref d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
      GG(ref c, d, a, b, x[3], S23, 0xf4d50d87); /* 27 */
      GG(ref b, c, d, a, x[8], S24, 0x455a14ed); /* 28 */
      GG(ref a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
      GG(ref d, a, b, c, x[2], S22, 0xfcefa3f8); /* 30 */
      GG(ref c, d, a, b, x[7], S23, 0x676f02d9); /* 31 */
      GG(ref b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */

      /* Round 3 */
      HH(ref a, b, c, d, x[5], S31, 0xfffa3942); /* 33 */
      HH(ref d, a, b, c, x[8], S32, 0x8771f681); /* 34 */
      HH(ref c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
      HH(ref b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
      HH(ref a, b, c, d, x[1], S31, 0xa4beea44); /* 37 */
      HH(ref d, a, b, c, x[4], S32, 0x4bdecfa9); /* 38 */
      HH(ref c, d, a, b, x[7], S33, 0xf6bb4b60); /* 39 */
      HH(ref b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
      HH(ref a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
      HH(ref d, a, b, c, x[0], S32, 0xeaa127fa); /* 42 */
      HH(ref c, d, a, b, x[3], S33, 0xd4ef3085); /* 43 */
      HH(ref b, c, d, a, x[6], S34, 0x04881d05); /* 44 */
      HH(ref a, b, c, d, x[9], S31, 0xd9d4d039); /* 45 */
      HH(ref d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
      HH(ref c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
      HH(ref b, c, d, a, x[2], S34, 0xc4ac5665); /* 48 */

      /* Round 4 */
      II(ref a, b, c, d, x[0], S41, 0xf4292244); /* 49 */
      II(ref d, a, b, c, x[7], S42, 0x432aff97); /* 50 */
      II(ref c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
      II(ref b, c, d, a, x[5], S44, 0xfc93a039); /* 52 */
      II(ref a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
      II(ref d, a, b, c, x[3], S42, 0x8f0ccc92); /* 54 */
      II(ref c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
      II(ref b, c, d, a, x[1], S44, 0x85845dd1); /* 56 */
      II(ref a, b, c, d, x[8], S41, 0x6fa87e4f); /* 57 */
      II(ref d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
      II(ref c, d, a, b, x[6], S43, 0xa3014314); /* 59 */
      II(ref b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
      II(ref a, b, c, d, x[4], S41, 0xf7537e82); /* 61 */
      II(ref d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
      II(ref c, d, a, b, x[2], S43, 0x2ad7d2bb); /* 63 */
      II(ref b, c, d, a, x[9], S44, 0xeb86d391); /* 64 */

      state[0] += a;
      state[1] += b;
      state[2] += c;
      state[3] += d;

      /* Zeroize sensitive information. */
      Array.Clear(x, 0, x.Length);
    }

    /* Encodes input (UINT4) into output (unsigned char). Assumes len is
       a multiple of 4. */
    private static void Encode(byte[] output,
                               uint[] input,
                               uint len)
    {
      for (uint i = 0, j = 0; j < len; i++, j += 4)
      {
        output[j] = (byte)(input[i] & 0xff);
        output[j + 1] = (byte)((input[i] >> 8) & 0xff);
        output[j + 2] = (byte)((input[i] >> 16) & 0xff);
        output[j + 3] = (byte)((input[i] >> 24) & 0xff);
      }
    }

    /* Decodes input (unsigned char) into output (UINT4). Assumes len is
       a multiple of 4. */
    private static void Decode(uint[] output,
                               byte[] input,
                               uint inputIndex,
                               uint len)
    {
      for (uint i = 0, j = 0; j < len; i++, j += 4)
      {
        output[i] = ((uint)input[inputIndex + j]) |
            (((uint)input[inputIndex + j + 1]) << 8) |
            (((uint)input[inputIndex + j + 2]) << 16) |
            (((uint)input[inputIndex + j + 3]) << 24);
      }
    }
  }
}